The present invention relates to thermal target simulation, in particular, it concerns generation of a thermal image by optical projection onto a surface.
Many systems, particularly weapon systems, operate by sensing, recognizing, analyzing, tracking, and/or homing in on a pattern of infrared (“IR”) radiation generated by a body at a raised temperature, or having a predefined temperature distribution. Such systems must be tested on thermal targets which simulate a range of intended operating conditions for the system.
The conventional approach for generating a thermal target is to employ a sheet or block of thermally conductive material of the required size and shape fitted with one or more heaters and having a thermostatic controller. Generally, the exposed surface area of the device renders it difficult to control the temperature of the body precisely, particularly under adverse environmental conditions such as exposure to wind or rain. Where a large target size is used, it can become particularly difficult to ensure high thermal stability and uniformity. Thermal target simulating devices are expensive to produce, and must be customized for each size and shape of target required. The costs of such devices is particularly problematic when performing weapon system tests wherein the target itself is destroyed during testing. In many cases, adjustment of the target temperature is also be very time consuming, taking as much as several hours to heat a target thoroughly, and even longer to allow cooling to a lower temperature.
For small targets, commercially available devices known as “extended blackbodies” provide a partial solution. These devices have an enclosed cavity with specially arranged and treated surfaces maintained at a constant temperature so as to generate an approximation to ideal “blackbody radiation” at an aperture. These extended blackbodies are readily controllable and offer a high stability and uniformity. Nevertheless, since the output aperture is much smaller than the dimensions of the device, currently available blackbody devices are limited to maximum target diameters of about 0.3 m. For extended (large) targets of dimensions over 0.5 m blackbody devices are not a feasible option.
For laboratory experiments, blackbody devices are sometimes combined with optical components such as collimators and patterned apertures for testing sensor properties. Such optical systems typically require that the optical components occupy the entire field of view of the sensor, and are therefore only feasible for controlled laboratory testing. Furthermore, even if used in the field, these optical systems are highly directional such that only a single sensor can typically view the target at a time. The optical components are also typically bulky and interfere with superposition of the target on a natural background.
Also known are controllable infrared display devices which can generate a dynamic display where individual pixels generate infrared under control of a processor system. Such devices are very costly, and still do not provide a viable solution for presenting a large target against a natural background.
There is therefore a need for a system and method for generating extended thermal targets which can be used to provide different sizes and/or shapes of target against a natural background. It would also be advantageous to provide a system and method for generating extended thermal targets which would provide rapid adjustability while ensuring high temperature resolution, high uniformity and high stability.